The (current) future of human spaceflight: the Space Launch System

NASA just announced its new program for human spaceflight: the Space Launch …

In the wake of the end of the Space Shuttle program, and the effective cancellation of the Constellation program, Americans (and the rest of the world) have been wondering what comes next. On Wednesday, NASA announced the Space Launch System (SLS), a new heavy-lift launch vehicle that will carry astronauts and cargo to low-Earth orbit (LEO), initially, and eventually beyond. This new vehicle, planned for a 2017 launch at the earliest, uses some components from previous designs (for instance, the engines from the Shuttle program and the Orion crew vehicle from Constellation) but is a new design, and it will be the most powerful rocket yet built. Let’s go over some of the (announced) details, and see what exactly NASA has come up with.

First: the hardware. NASA focused on a design that would be both modular, combining different components for different missions, and reuse existing designs. The main engines will all be liquid-fueled, using hydrogen and oxygen (like the Space Shuttle main engine). To avoid the unnecessary expense of entirely new engines (see the Ares rockets), the new vehicle will use the RS-25 engines from the Space Shuttle main engines for the core stage and the J-2X, a variant of the J-2 engine from the Apollo-era Saturn V rockets, for the upper stage. The J-2X was originally designed for the Constellation program as a cheaper and more efficient engine compared to those used in the Space Shuttle.

The initial (announced) design will have a payload capacity of 70 metric tons (154,000 pounds), with a fully fueled liftoff weight of 5.5 million pounds (about 2500 metric tons), and use three RS-25 engines for a single stage, with solid rocket boosters similar to those used on the Shuttle. With additional boosters, this design could support 100 metric tons. Later, by adding two more RS-25 engines and an upper stage J-2X engine, the payload capacity will be upgraded to 130 metric tons (268,000 pounds). For some perspective, the three-stage Saturn V rocket used in the Apollo missions (the most powerful ever used, and hasn’t been used since 1973) has a maximum payload capacity of 119 metric tons.

For those unfamiliar with the concept of rocket staging, here’s a quick explanation. Chemical rockets basically generate thrust by expelling mass; in fact, the propellant mass is typically much larger than the actual payload and structure of the vehicle (for instance, propellant makes up 80 percent of the mass of the fully fueled Space Shuttle system at launch). In order to avoid carrying up unnecessary structural mass (which in turn requires additional propellant, and so on), rocket designers employ staging, where the entire vehicle is broken into self-contained stages that disconnect when their propellant is exhausted—think of the boosters and external tank falling off once the Shuttle gets to a certain altitude. Multiple stages increases complexity, but this is considered a worthy tradeoff when compared against considerable added propellant.

Now, where exactly is this vehicle going to take us? This part is a little more ambiguous. NASA plans on using the six-person Orion crew vehicle, now known as the Multi-Purpose Crew Vehicle (MPCV), with the SLS. The initial design could carry astronauts and cargo to LEO, where the International Space Station (ISS) and most satellite are located—but NASA is planning on using commercial spaceflight companies like SpaceX and Orbital Sciences to resupply the ISS, and their vehicles will be ready sooner than the SLS.

That leaves near-Earth asteroids, cis-lunar space, the Moon, and beyond (think Mars) for the SLS. I’m sure we’ll hear more about the destinations as the initial launch date (2017) approaches, but it is exciting to see that NASA has come up with a solid design, especially one that reuses known elements. The modularity of the design also allows for different missions, just by adding more boosters and an upper stage. Hopefully this pragmatism will allow this program to avoid the sweeping budget cuts of the current US government.

Kyle Niemeyer
Kyle is a science writer for Ars Technica. He is a postdoctoral scholar at Oregon State University and has a Ph.D. in mechanical engineering from Case Western Reserve University. Kyle's research focuses on combustion modeling. Emailkyleniemeyer.ars@gmail.com//Twitter@kyle_niemeyer

104 Reader Comments

Unfortunately if Obama loses the 2012 election, the date slips significantly beyond 2017, or congress crushes the program by failing to provide enough funding to meet milestones; it will end up along side every other shuttle replacement in the graveyard of cancelled NASA programs.

"Multiple stages increases complexity, but this is considered a worthy tradeoff when compared against considerable added propellant."

Multiple stages are required for lofting large payloads into orbit. With today's technology (specific impulse), a singe stage rocket couldn't launch even a ton into orbit, regardless of how much propellant you throw at it. So it's not such much a worthy tradeoff as much as an absolutely necessary one. Still, good explanation of staging, I don't see that in news articles very often.

Posted: 19 Sep 2011 15:15 Weren't the engines from the Space Shuttle based on von Braun's original designs from the 60's?

Have there really been no advances since then?

SSME's were designed in the 70's and use a different, more advanced engine cycle than the J-2's used on the Saturn V (closed-loop cycle with preburners, as opposed to open loop gas generator cycle). I'm not sure what von Braun's role was in J-2/SSME, but I can assure you that many upgrades have been made to the SSME since it was first designed. It is a very efficient engine.

It's also worth noting that developing a new engine involves a significant effort and would probably cost billions of dollars. It's a lot easier to use one that works and is available.

I think I read somewhere that the Falcon Heavy would be an even better alternative to SLS. Cheaper & with a higher payload capacity.

Can someone confirm?

Cheaper sure, but max payload capacity on Falcon Heavy is somewhere around 50 tons if I recall correctly. Also in SpaceX's press release about the Falcon Heavy, they mentioned that it is not designed to compete with SLS and they fully support NASA developing a heavy lift booster on their own.

"Multiple stages increases complexity, but this is considered a worthy tradeoff when compared against considerable added propellant."

Multiple stages are required for lofting large payloads into orbit. With today's technology (specific impulse), a singe stage rocket couldn't launch even a ton into orbit, regardless of how much propellant you throw at it. So it's not such much a worthy tradeoff as much as an absolutely necessary one. Still, good explanation of staging, I don't see that in news articles very often.

The single stage Viking 7 reached an altitude of 136 miles on 7 August 1951. It had a mass ration of 5:1.

"Multiple stages increases complexity, but this is considered a worthy tradeoff when compared against considerable added propellant."

Multiple stages are required for lofting large payloads into orbit. With today's technology (specific impulse), a singe stage rocket couldn't launch even a ton into orbit, regardless of how much propellant you throw at it. So it's not such much a worthy tradeoff as much as an absolutely necessary one. Still, good explanation of staging, I don't see that in news articles very often.

The single stage Viking 7 reached an altitude of 136 miles on 7 August 1951. It had a mass ration of 5:1.

Right, it did not enter orbit. If by mass ratio you mean mass fraction, 80% is extremely low. Good rocket designs will have mass fractions closer to 90% or above (that's the ratio of the weight of the fuel to the weight of fuel + structural weight, i.e. tanks, plumbing, engines, stuff that doesn't get burnt up, etc.)

One could argue that the SLS is an implementation of the DIRECT design proposal. So, it might be better to say that SLS is what some NASA engineers (and others) came up with on their own time during the failure of Constellation as an alternative.

Unless they come up with a specific goal for this rocket they are going to have a very hard time maintaining a consistent funding level for the next 5 years. They need a hard timeline, and they need to stick to it.Still, its nice to see some work in the super-heavy rocket class.

The Space Frontier Foundation attacks this system intensly, headlining an article "Monster Rocket Will Eat American Space Program." Other sources say the Obama administration is already trying to kill the program. Personally I was excited by the design decisions but some in the private sector see the funding to develop the SLS as competition for their pending and future contracts and are attacking it like the Right attackes taxes. The entire article is so vehement as to destroy its credibility.

Unfortunately if Obama loses the 2012 election, the date slips significantly beyond 2017, or congress crushes the program by failing to provide enough funding to meet milestones; it will end up along side every other shuttle replacement in the graveyard of cancelled NASA programs.

And you know this how ? Are you Obama's spending aid. Do you know who is going to win already ? You are guessing on a variable that Vegas wouldn't take odds on.

What changed compared to Ares V? It is not clear.Wasn't Ares V supposed to be based on the Shuttle engines too?

I don't recall that a specific design was chosen for Ares V, at least in terms of RS-68 vs. SSME. Also Ares V was supposed to have a larger diameter tank (10m as opposed to Shuttle's and SLS's 8.4m, but those are from memory so someone please correct me if I'm mistaken). One more thing: Ares V was not meant to be launched in such an evolvable form, with a 70t launch then a 100t then a 130t.... It was going to have an initial (and final) payload capacity somewhere in the neighborhood of 180t, if I recall correctly.

You'll notice that 2017 is followed by "at the earliest"... i.e. it's a wishy-washy BS number that no one can be held accountable for and is just meant to grease the current budgetary process and avoid the inevitable questions about why did we (really) cancel the Constellation heavy lift platform in the first place. I blame Elon Musk and his salesmanship, but hopefully SpaceX can actually deliver on their promises and NASA's fears are unfounded (but not before we spend tens of billions of dollars on a regurgitated platform rather than the future "based on new technology" platform that we were sold).

The single stage Viking 7 reached an altitude of 136 miles on 7 August 1951. It had a mass ration of 5:1.

As mentioned by Nickolai, the Viking 7 was a sounding rocket that went straight up, and then back down. 136 miles amounts to roughly 2km/s of delta-v, while low Earth orbit is closer to 11km/s. Recall that fuel requirements grow exponentially with final velocity, not linearly. That's why people are less than impressed by the whole sub-orbital craze and SpaceShipOne. It's no small feat, sure, but it's one we've been doing since the 50s.

The single stage Viking 7 reached an altitude of 136 miles on 7 August 1951. It had a mass ration of 5:1.

As mentioned by Nickolai, the Viking 7 was a sounding rocket that went straight up, and then back down. 136 miles amounts to roughly 2km/s of delta-v, while low Earth orbit is closer to 11km/s. Recall that fuel requirements grow exponentially with final velocity, not linearly. That's why people are less than impressed by the whole sub-orbital craze and SpaceShipOne. It's no small feat, sure, but it's one we've been doing since the 50s.

Wagnerrp, I think you're confusing LEO dV with escape velocity - to be in a low earth orbit you need around 7.8 km/s of dV.

I also think it's worth noting that the date C Boy provides is 6+ years before Sputnik, so we already know if didn't reach orbit without any technical details

SpaceX's development of a 53mT launch vehicle would change things, especially as the proposed launch costs would be significantly less than what the SLS will cost. Not to mention that the US taxpayer isn't paying anything for development of the Falcon Heavy. It's entirely possible that a Falcon heavy will fly before any SLS design.

One important thing the article left unsaid is that the SLS derives most of it's thrust (and weight, hehe) from the pair of solid rocket boosters (SRB's). The SLS uses a newer, more powerful version (5 segments, instead of 4) of the boosters that the Shuttle used. The only staging used for the 70 mT version would be the SRB's dropping off after they've expended their thrust.

It's important to note that the SLS requires boosters for launch because the SLS design allows for the replacement of the original SRB's with other potential boosters after the initial design is certified. This implies that other vendors could attempt to compete with current SRB vendor ATK for SLS service and might be able to reduce the cost of each launch with less expensive boosters in the future. This is a large change from the Shuttle program where each vendor was set in stone, and had less incentive to produce less expensive components.

There are designs already proposed that would use liquid rocket boosters (LRB's) derived from the Atlas and Falcon 9's launchers. The LRB's produce less thrust, but weigh considerable less so the added lift is comparable.

With 2 viable heavy lift programs in development, these are good times to be a space flight enthusiast.

Bush / Obama, or Republicans / Democrats, are just playing tennis with NASA budget & programmes. They're just trying to score political points by saddling each other's balance-sheets with expensive white elephants (or otherwise, gain credit for their forward-looking "vision" whilst challenging their successors in the US Presidency to lose face by cancelling the useless programme). They're trying to push expenses onto each other's tab. Only, instead of pointing this out, everyone seems distracted with the "tech specs" and ideological "vision" of it all. Instead of calling out the Republicans' hypocrisy, the Democrats are now trying to get their own back. Is it any coincidence that Bush's vision of space exploration was scheduled to be paid-for by Obama, or that Obama's vision will probably be paid-for by a Republican successor (acceding either now or in 2016)?

Obama's excuse for cancelling Ares? He claimed it didn't have enough new technology in its design; it wasn't bold enough. It was just a repeat of Apollo, with the same old boring liquid hydrogen technology... But now, he's laying out a grand new vision for a programme that's almost identical to Ares, except that it has even LESS new technology in it, and the liquid hydrogen technology is being promoted as one of the strengths of the project! SLS's heavy-lifting capability is even more similar to Saturn V than is Ares's!!!

SLS might be cancelled soon after the Republicans get back in power. They will say it's a castrated version of Ares, with less heavy-lifting capability, that won't be able to do the missions it's commissioned to do (Mars, asteroids, permanent lunar bases...) Then they'll reinstate Ares and set the programme schedule so the budget will only start to draw big dollars from the government's coffers once the Democrats get back in power...

There are designs already proposed that would use liquid rocket boosters (LRB's) derived from the Atlas and Falcon 9's launchers. The LRB's produce less thrust, but weigh considerable less so the added lift is comparable.

With 2 viable heavy lift programs in development, these are good times to be a space flight enthusiast.

It's also worth noting that liquid engines almost always have a higher specific impulse than solid rockets. This means basically that you get more delta-V per kg of liquid propellant than you do per kg of solid propellant.

So even though the liquid's are producing less thrust, a higher percentage of that thrust is going towards increasing the speed of the rocket.

Also, liquid fuels are really cheap, pennies on the gallon. Solid fuels are much more expensive (of course liquids require complicated engines which adds to their cost).

And yes, it's a pretty good time to be a space flight enthusiast, especially if Blue Origin gets serious about their resuable booster system.

Ares started a bit like this, then they decided they needed something bigger to go to Mars in one shot (Bush's dream), so they scrapped most of the Shuttle commonality.

Then the DIRECT guys came along proposing, basically, the SLS.

Then NASA proceeded post-haste to stop all Shuttle manufacturing, to release more money to Ares and indirectly kill DIRECT (which tried to use mostly unmodified Shuttle parts). Shuttle manufacturing plants and contracts were stopped, and people laid off.

Then Ares was too expensive as well and NASA ended up with nothing.

Then Obama killed Kennedy Space Center and decided to wait for private rockets and get russian rides in the meantime.

Then Congress mandated NASA to investigate a laucher using mainly Shuttle parts. NASA hemmed and hawed trying to not build DIRECT after having bitchslapped it for the last four years.

Then the russians grounded all manned flights last month after problems with their launcher's third stage.

Enter the "Jobs Programme Launcher by CongressTM" (SLS), retreading DIRECT (but painting it like a Saturn V for PR).

The single stage Viking 7 reached an altitude of 136 miles on 7 August 1951. It had a mass ration of 5:1.

As mentioned by Nickolai, the Viking 7 was a sounding rocket that went straight up, and then back down. 136 miles amounts to roughly 2km/s of delta-v, while low Earth orbit is closer to 11km/s. Recall that fuel requirements grow exponentially with final velocity, not linearly. That's why people are less than impressed by the whole sub-orbital craze and SpaceShipOne. It's no small feat, sure, but it's one we've been doing since the 50s.

Wagnerrp, I think you're confusing LEO dV with escape velocity - to be in a low earth orbit you need around 7.8 km/s of dV.

That seems awfully low. Low Earth (~200km) orbital velocity alone is going to be 7.8km/s, and starting from the ground, the most you're going to get from initial rotation is around 0.45km/s. Getting to altitude costs you around 2km/s as mentioned above, plus another 1-1.5km/s for aerodynamic losses on the way up.

The single stage Viking 7 reached an altitude of 136 miles on 7 August 1951. It had a mass ration of 5:1.

As mentioned by Nickolai, the Viking 7 was a sounding rocket that went straight up, and then back down. 136 miles amounts to roughly 2km/s of delta-v, while low Earth orbit is closer to 11km/s. Recall that fuel requirements grow exponentially with final velocity, not linearly. That's why people are less than impressed by the whole sub-orbital craze and SpaceShipOne. It's no small feat, sure, but it's one we've been doing since the 50s.

Wagnerrp, I think you're confusing LEO dV with escape velocity - to be in a low earth orbit you need around 7.8 km/s of dV.

That seems awfully low. Low Earth (~200km) orbital velocity alone is going to be 7.8km/s, and starting from the ground, the most you're going to get from initial rotation is around 0.45km/s. Getting to altitude costs you around 2km/s as mentioned above, plus another 1-1.5km/s for aerodynamic losses on the way up.

Why does getting to altitude cost 2km/s more than LEO requirements? Also, drag losses are on the order of 100-200m/s, not 1km/s.

You are correct in that I didn't consider losses, 7.8km/s is the 'exact' delta-V required for ~200km LEO. But gravity and drag losses would put that a touch over 8km/s, and then rotation benefits, as you mentioned, would probably bring it down to below 8 km/s

Ares started a bit like this, then they decided they needed something bigger to go to Mars in one shot (Bush's dream), so they scrapped most of the Shuttle commonality.

Then the DIRECT guys came along proposing, basically, the SLS.

Then NASA proceeded post-haste to stop all Shuttle manufacturing, to release more money to Ares and indirectly kill DIRECT (which tried to use mostly unmodified Shuttle parts). Shuttle manufacturing plants and contracts were stopped, and people laid off.

Then Ares was too expensive as well and NASA ended up with nothing.

Then Obama killed Kennedy Space Center and decided to wait for private rockets and get russian rides in the meantime.

Then Congress mandated NASA to investigate a laucher using mainly Shuttle parts. NASA hemmed and hawed trying to not build DIRECT after having bitchslapped it for the last four years.

Then the russians grounded all manned flights last month after problems with their launcher's third stage.

At this point, I'd argue that SLS is best possible design that could have come from NASA at this point in time, given the Congressional mandate and the, um, interesting history you list. While NASA seems to abhor the thought that DIRECT was a good design, they do seem to have bitten the bullet and designed the SLS around it.

SLS still provides jobs to various states, but many would argue that NASA only keeps it's funding that way. That's why I like SpaceX. They are providing a purely commercial heavy launch vehicle that is "not in competition" with SLS, but provides a shiny example as how to do a launch vehicle.

I think the US and NASA kinda rested on their laurels with the Shuttle the last few years. Competition and alternative programs can be an effective way to get your engineering teams motivated to perform.

I think I read somewhere that the Falcon Heavy would be an even better alternative to SLS. Cheaper & with a higher payload capacity.

Can someone confirm?

Cheaper sure, but max payload capacity on Falcon Heavy is somewhere around 50 tons if I recall correctly. Also in SpaceX's press release about the Falcon Heavy, they mentioned that it is not designed to compete with SLS and they fully support NASA developing a heavy lift booster on their own.

Oddly not a word about SpaceX doing the same thing in 3 years 140 tons LEO with the Falcon X at a fraction the cost.

They drill a hole in a salt formation. Put a small nuke at the bottom in a water tank, put a thick steel plate on top of the tank with a automated payload capsule on top. Light the nuke and let er rip.

3000 tons at $10 a lb straight to the moon. I'm sure the Chinese are drilling while we twiddle our thumbs.

I think I read somewhere that the Falcon Heavy would be an even better alternative to SLS. Cheaper & with a higher payload capacity.

Can someone confirm?

Cheaper sure, but max payload capacity on Falcon Heavy is somewhere around 50 tons if I recall correctly. Also in SpaceX's press release about the Falcon Heavy, they mentioned that it is not designed to compete with SLS and they fully support NASA developing a heavy lift booster on their own.

Oddly not a word about SpaceX doing the same thing in 3 years 140 tons LEO with the Falcon X at a fraction the cost.

They drill a hole in a salt formation. Put a small nuke at the bottom in a water tank, put a thick steel plate on top of the tank with a automated payload capsule on top. Light the nuke and let er rip.

3000 tons at $10 a lb straight to the moon. I'm sure the Chinese are drilling while we twiddle our thumbs.

They will launch a few nuclear engines from stolen updated NASA Nerva designs and be flitting around the Solar system in no time.

Falcon X requires a new engine, the Merlin2. Let me know when SpaceX has even started that development program. I think they're plenty busy with Falcon 9 and Falcon Heavy at the moment.

As for the Chinese, I've seen no evidence that are doing anything unconventional with their space program.

I looked at your link and noticed a rather gaping hole in that program- if you launch your vehicle with a 3000G (yep, that's correct, 3K G's) acceleration, what are you going to use to kill it's DeltaV once it leaves Earth orbit? No current rocket engine design could survive that intact, so how do you maneuver the vehicle after launch?

17 G$ for two launches? Plus the inevitable doubling or trebling in cost overruns?

That's 17 G$ for about 140 tons to orbit. That same 17 G$, at 100 M$ per launch, could pay for 170 Falcon Heavy launches. That's roughly 9,000 tons to orbit. If your cargo could be made at all modular, it would still be much cheaper to send it up on multiple Falcon Heavies, even adding in the cost of orbital assembly!

The real problem with SLS is the lack of a clear vision for what it is supposed to do. What requirements drive the 70 and 130 ton lift masses? For any small to medium payloads, an Atlas or Falcon will be far cheaper. For large payloads which can be modularized and assembled on orbit, a series of Atlas or Falcons will do quite well. So, what's the driver for launching really big things all in one go? That is the only real reason to have SLS (that, and the jobs program, which I happen to agree is important these days, actually.)

Even if SpaceX botches the cost of a Falcon 9 Heavy by a factor of 4 from their stated estimates, you'd get 53 tons to orbit for ~$400M, or 150 tons for $1.2B, which is still cheaper than an SLS launch is likely to be. Remember, the space shuttle was $1.5B/launch and the SLS is not doing things all that much different than the STS.